1. Field of the Invention
The present invention relates to an apparatus for supplying a fuel to a combustion type of vehicular heater (hereinafter called a vehicular combustion heater). The apparatus is mounted mainly on an electric vehicle for the purpose of heating the cabin of the vehicle.
2. Description of the Related Art
A vehicular combustion heater which is mounted on a vehicle is supplied with a fuel from a fuel tank via a fuel pump. In order to protect the fuel tank, there is interposed a two-way valve in a vent passage which is connected to the fuel tank and which is also open to the atmosphere. This two-way valve has a positive pressure valve which opens when an internal pressure in the fuel tank has reached a positive pressure above a predetermined value, and a negative pressure valve which opens when the internal pressure in the fuel tank has reached a negative pressure exceeding (i.e., lower than) a predetermined value.
The electric vehicle has an object of preventing the atmosphere from being polluted. Therefore, in order to minimize the discharging of the fuel vapor from the fuel tank into the atmosphere to the best extent possible, it is required to set a set pressure of opening the above-described positive pressure valve at a high value.
However, if the set pressure to open the positive pressure valve is made high, the fuel is pushed by the internal pressure of the fuel tank when the vehicular combustion heater is not in use. Consequently, the fuel leaks out of the fuel pump into the vehicular combustion heater. The fuel vapor is then discharged into the atmosphere from the vehicular combustion heater. More particularly, when the vehicle is inclined on a slope or the like whereby a rollover valve in a vent passage which is provided in the fuel tank and which is open to the atmosphere is blocked, the fuel is likely to flow into the vehicular combustion heater due to a syphon effect. As a result, the amount of discharge of the fuel vapor into the atmosphere increases.
In view of the above points, the present invention has an object of providing an apparatus for supplying a fuel to a vehicular combustion heater in which the discharging of the fuel vapor from the vehicular combustion heater into the atmosphere is minimized to the best extent possible.